Iron Content of Saccharomyces cerevisiae Cells Grown under Iron-Deficient and Iron-Overload Conditions

Abstract

Fermenting cells were grown under Fe-deficient and Fe-overload conditions, and their Fe contents were examined using biophysical spectroscopies. The high-affinity Fe import pathway was active only in Fe-deficient cells. Such cells contained ~150 μM Fe, distributed primarily into nonheme high-spin (NHHS) FeII species and mitochondrial Fe. Most NHHS FeII was not located in mitochondria, and their function is unknown. Mitochondria isolated from Fe-deficient cells contained [Fe4S4]2+ clusters, low- and high-spin hemes, S=½ [Fe2S2]1+ clusters, NHHS FeII species, and [Fe2S2]2+ clusters. The presence of [Fe2S2]2+ clusters was unprecedented; their presence in previous samples was obscured by the spectroscopic signature of FeIII nanoparticles which were absent in Fe-deficient cells. Whether Fe-deficient cells were grown under fermenting or respirofermenting conditions had no effect on Fe content; such cells prioritized their use of Fe to essential forms devoid of nanoparticles and vacuolar Fe. The majority of Mn ions in WT yeast cells was EPR-active MnII and not located in mitochondria or vacuoles. Fermenting cells grown on Fe-sufficient and Fe-overloaded medium contained 400 – 450 μM Fe. In these cells the concentration of nonmitochondrial NHHS FeII declined 3-fold, relative to in Fe-deficient cells, whereas the concentration of vacuolar NHHS FeIII increased to a limiting cellular concentration of ~ 300 μM. Isolated mitochondria contained more NHHS FeII ions and substantial amounts of FeIII nanoparticles. The Fe contents of cells grown with excessive Fe in the medium were similar over a 250-fold change of nutrient Fe levels. The ability to limit Fe import prevents cells from overloading with Fe.

Mitochondrial Iron-Sulfur Cluster Activity and Cytosolic Iron Regulate Iron Traffic in Saccharomyces cerevisiae

“…These reporter proteins develop activity at rates and to extents that are proportional to [Fe med Mitochondria are the major iron traffic hubs in eukaryotes. The organelle from respiring yeast cells grown in iron-sufficient medium contains 500 -800 M iron, most of which is present as Fe 4 S 4 clusters and heme centers housed in respiration-related proteins (5). [Fe 2 S 2 ] 1ϩ/2ϩ clusters and Fe III phosphate oxyhydroxide nanoparticles are also present.…”

“…Much of the remaining intensity arises from mitochondrial iron, including a central quadrupole doublet that arises from [Fe 4 In our studies, the overall concentration of iron in cells grown on iron-deficient, iron-sufficient, and iron excess conditions is ϳ 200, 400, and 600 M iron, respectively. Iron-deficient cells are largely devoid of vacuolar iron; their Mössbauer spectra are dominated by the central doublet and an unusually strong NHHS Fe II doublet (5). Mitochondria isolated from iron-deficient cells contain less iron than do mitochondria from iron-sufficient or iron-excess ones (ϳ400 M versus 700 -800 M), but they contain similar levels of respiration-related ISCs and heme centers.…”

Contribution of Mössbauer spectroscopy to the investigation of Fe/S biogenesis

“…All the studies performed evidenced that the accumulation of iron in the cytosol is prevented because of the potential damages that Fe II ions can cause. Accordingly, it was proposed that the excess of iron is exported either into vacuoles or into mitochondria, to detoxify the cytosol [71, 72]. …”

“…It was proposed that it serves as an iron pool for the biosynthesis thereof [68, 73]. Similar species were proposed to be present in the cytosol [72], their amount being more important under iron-deficient growth conditions [71]. Moreover, it is suspected that another non-heme high-spin Fe II species is present in vacuoles of cells depleted of the vacuolar iron importer CCC1 [66].…”

Responses of Saccharomyces cerevisiae Strains from Different Origins to Elevated Iron Concentrations

“…The utilization of biophysical spectroscopies has recently allowed the detailed examination of yeast iron contents in terms of growth phase, chemical form, and distribution within organelles (25,26,29). In the exponential growth phase, the intracellular yeast iron level remains roughly constant due to a balance between iron import and cellular division (26).…”